Powerpoint for electricity and magnetism

1. Electricity and Magnetism
Magnets are like electrically charged objects in that like ends
of the magnet repel(north repels north and south repels
south)and unlike ends of the magnet attract ( north is
attracted to south). There are two types of magnets: (1)
Permanent magnets–are an alloy of iron and lodestone or
magnetite . Permanent magnets occur naturally and (2)
electric magnets – they are man made and are created by
pushing electrons through wire wound in a coil. Pushing more
current and creating more coils makes the electric magnet
stronger.

2. All magnets have a limited region around them in
which they will push or pull other magnetic objects
and this region is called the Magnetic field . The
magnetic field is strongest at the north and south
poles of the magnet. All magnets have a north and
south pole. One large magnet can be broken into
many small magnets and each of the small magnets
will still have a north and south pole.

3. The earth is a giant magnet with a north and a south
pole. The geographic north pole (Alaska) is actually
the magnetic south pole and the geographic south
pole (Antarctica) is actually the magnetic north pole.
A Compass is a magnet free to spin and the
compasses north magnetic pole is attracted to and
will spin until it points to the earth’s magnetic south
pole.

4. Nails and other iron objects can be made into temporary
magnets. Temporary magnets and permanent magnets have
their atoms with aligned magnetic poles, these aligned
Magnetic poles are called the magnetic domains. If you
strike temporary or permanent magnets hard or often their
atoms will get out of alignment and will cause the object to
lose its magnetic properties. Heating a magnetic will also get
its magnetic domains out of alignment and it will no longer be
a magnet.

5. We have already stated that electric current moving
through a wire produces a magnetic field. The
direction the current moves determines the poles of
the magnet. Reversing the current direction reverses
the poles. Electromagnets are very useful because
their poles are easily reversed by flipping a switch to
reverse current direction. They can be turned on and
off by starting and stopping the current and they can
be made stronger or weaker by increasing or
decreasing the amount of current.

6. The modern world could not operate without
electromagnets. All meters that measure electricity use
a permanent magnet and a electromagnet. The
electromagnet is free to turn or pivot and is attached to
the needle or arm of the meter. The electromagnet
does not become a magnet until current runs through
it, the more current the stronger the electromagnet
becomes and the further the needle moves. The meter
is calibrated to measure this force of attraction between
the electromagnet and the permanent magnet.

7. Meters are wired with different circuits to
allow them to measure different properties
of electricity. Ammeters –are wired in
series to measure the total number of
electrons flowing through a wire.
Ammeters measure current in amps.
Voltmeters measure the push on electrons
in volts and are wired in parallel to
measure the push in each separate branch
of the circuit. Ohm meters – measure
resistance in ohms.

8. Motors- also use an electromagnet and a permanent
magnet to turn electrical energy into mechanical energy or
motion. Electric motors are found in most household
appliances such as: fans, blenders, vacuum cleaners, etc. The
electromagnet in motors has its poles reversed by a
commutator which is a switch that rotates with the
electromagnet. The north end of the permanent magnet
attracts and pulls the south end of the electromagnet. When
the south and north ends line up the commutator reverses
the current which reverses the poles..

9. Now north and north are aligned. These two
like poles repel which pushes the
electromagnet, that is attached to a turning
shaft, away completing the circle. The
commutator will again switch current ,which
switches poles, and the process continues
much like a dog chasing his tail. Coiling the
wire cause the magnetic fields to overlap and
this produces a stronger magnet than current
running through a straight wire produces

10. Most electricity comes from burning coal which turns the
chemical potential energy of coal into thermal energy of
heat and steam. The thermal energy of steam is used to
turn turbine blades. This moving turbine is mechanical
energy and it is used to move a magnet inside a coil of
wire which generates electricity. Electrical energy can
then be converted into sound energy with a CD player,
heat, or almost any other form of energy. Once scientists
learned that moving electrons (electricity) could become
a magnet (electromagnet), they then discovered that
moving a magnet inside a coil of wire could cause the
electrons in the wire coil to move creating electricity. This
process is called electromagnetic induction and use a
magnet and a coil of wire called a solenoid to produce a
constant electric current.

11. Reversing the pole
on the magnet
causes the direction
of electric current to
reverse. Moving the
magnet back and
forth can produce
alternating current
A/C.

12. A generator is a device that produces electricity by rotating a coil of
wire inside a magnetic field. It is just the opposite of an electric
motor (which turns electricity into motion). A generator turns motion
into electricity (mechanical energy into electrical energy). The power
companies use the motion of water flowing over a dam, or they
create steam to spin their turbines. Wind from windmills can also be
used to spin electrical turbines. Batteries, like generators will cause
electrons to move along a wire producing electricity. Except batteries
produce direct current D/C while generators produce alternating
current A/C. Electricity produced by power company generators
produce A/C current that alternates 120 times a second or is on 60
cycles( 60 Hz).

13. To get electricity to travel from the power company to
your house it has to be pushed with high voltage. This
much voltage must then be decreased before it enters
your house, for safety reasons. A Transformer can
increase or decrease voltage --or the push on
electrons. A step up transformer increase voltage and
a step down transformer decreases voltage. These
transformers will work either way depending on the
direction the current enters the transformer.
Examples of transformers can be found on the tops of
telephone poles and look like trash barrels attached
to the pole. Transformers work by increasing or
decreasing the number of electrons being pushed
down a wire..

14. To increase the number of electrons we increase the number
of wire coils. To decrease the number of electrons we
decrease the number of wire coils. Both coils (primary and
secondary) must be attached to the same piece of iron core
which will become a magnet when either coil has electricity
running through it. Alternating current will cause the
electrons in the iron core (now an electromagnet) to move
back and forth. These moving electrons have the same effect
as moving the magnet itself and moving the magnet will
cause the electrons in the wire coil to move.
Step down transformer Step up transformer

15. Any amount of voltage can be produced in a transformer
by adding or subtracting coils of wire. Direct current
cannot be used in a transformer because the magnetic
field produced by D/C current doesn’t reverse its poles
like alternating current does.
All conductors currently used to carry electricity have
some resistance and resistance causes some of the
electrical energy to be wasted as heat or thermal energy.
It has recently been discovered that cooling certain
materials to near absolute zero (0 Kelvin) will cause the
material to become a Superconductor – and offer no
resistance to electricity. Superconductors lose no
electricity as heat unlike copper wire which can lose 10%
of the electrical energy to heat energy

16. . The main problem with superconductors are that they have
to be very cold, and superconductor materials are often
brittle and hard to shape into wire. Experiments have been
performed that cause passenger trains to Levitate – float in
air using magnetic forces. The train has large magnets
attached to their side, underside and the rails (track) is also
made of a superconductor that becomes a very powerful
electromagnet. The two magnets (Train and Track) repel each
other making the trains levitate. The train then travels with
only the friction of air.

17. Four forces of nature
• 1) Gravity—force of attraction between
objects with mass.
• 2) Magnetism—force of attraction between
opposite poles of a magnet (N and S ) and
force of repulsion between like poles of a
magnet.(N and N or S and S )
• 3) Weak force—force of attraction between
oppositely charged particles (+ and - ) and
force of repulsion between like charges (+ and
+ or – and - )
• 4) Strong Force– nuclear force that holds
protons together in nucleus of atoms